WASHINGTON
- The female hormone estrogen can bend the gender of male fish that
live in bodies of water contaminated with the residue of birth-control
pills, a new study indicates.

For
three years, Canadian scientists have put birth-control pills into
a remote Ontario lake to measure this impact. The results: All male
fish in the lake - from tiny tadpoles to large trout - were "feminized,"
meaning they had egg proteins growing abnormally in their bodies.

The
experiment was intended to match the impact that the female hormone
estrogen may be having on many American bodies of water, as city
sewage systems empty waste into them that is contaminated with residue
from birth-control pills.

One-third
of male Pearl Dace minnows grew eggs in their testes. The entire
population of the common Fathead minnow, once numbering in the several
thousands, crashed to near zero because the hormone-stoked fish
couldn't reproduce.

"Any
fish species we have in the lake, any male is responding to the
estrogen," said Karen Kidd, a research scientist at the Canadian
Freshwater Institute and the study's chief researcher. She presented
her findings to the American Chemistry Council this week. "It
is a feminization. ... It's enough to be concerned about what's
going on in the bigger picture (from estrogen)."

Kidd's
research - the most controlled experiment ever to look at the effects
of estrogen on ecosystems - has heightened concerns that human female
hormones may be hurting wildlife, said several scientists in the
U.S. government.

Scientists
are looking at whether estrogen and chemicals that act like estrogen
are affecting human males, as well, said Mike Mac, the director
of the U.S. Geological Survey's Columbia Environmental Research
Center. He noted that a study earlier this month in the journal
Environmental Health Perspectives found that rural men exposed to
certain pesticides that act like estrogen had lower sperm counts.

Kidd's
$925,000 study is mostly funded by the Canadian government, with
help from the U.S. Environmental Protection Agency and private industry.

Estrogen
gets into waterways through a familiar path. Millions of women take
different types of estrogen in birth-control pills and hormone replacement
therapy; Kidd's study used the synthetic estrogen called ethynylestradiol,
or EE2. When the women urinate, the estrogen passes into sewer systems,
where bacteria eat much but not all of it. The remaining estrogen
leaves sewage-treatment plants and flows into rivers, lakes and
streams along with the treated wastewater.

"We
do not have a good handle on what's (coming out of) these sewage
treatment plants in this country yet," said Jim Lazorchak,
the acting chief of the EPA's molecular ecology branch in Cincinnati,
who has worked with Kidd on the lake experiment. "This is a
very emerging issue."

Scientists
have suspected for years that estrogen from humans is at least partially
to blame for strange animal sexual oddities - such as hermaphrodites,
which have both male and female characteristics - but other hormones
and common chemicals also are thought to disrupt animals' endocrine
systems. As a result, scientists have had a difficult time finding
a direct cause-and-effect example in the wild. Kidd's study shows
that link.

The
clarity of the result stems from the fact that Kidd used Canada's
unique Experimental Lakes Area, a range of 85 unpolluted lakes hours
from any city. For 35 years the Canadian government has set it aside
for experiments in environmental science.

Since
2001, Kidd and her colleagues have put birth-control pills into
one lake three times a week every summer. She then compared the
fish in the lake to those they found there in 2000 and to those
in two control lakes where no estrogen was added.

Kidd
seeded the lake with 5 nanograms of EE2 for every liter of water,
a level roughly equivalent to a typical U.S. urban waterway, said
Larry Barber, a USGS geochemist who studied the prevalence of estrogen
in 70 U.S. rivers, lakes and streams. In Barber's study, four U.S.
sites - in Florida, New York state, Massachusetts and Montana -
had EE2 levels many times higher than in Kidd's lake. The Florida
site, near Moriczville, had 273 nanograms per liter, according to
Barber's study.

"The
study in the experimental lakes shows that EE2 as an environmental
contaminant has an important ecological impact," Barber said.
"This is an issue in the U.S."

But
there's hope, Kidd said.

Bacteria
that occur naturally in lakes and are used for treatment in sewer
plants consume the estrogen in water. The answer to the estrogen
problem in waterways could be simply to arrange for more prolonged
bacteria treatment in sewer plants, she said.

"These
are issues that are starting to come to the fore a little bit more
now," said Adam Krantz, a spokesman for the Association of
Metropolitan Sewerage Agencies. "We're waiting to see what
the science shows us. We're tracking it."